Tamoxifen, a nonsteroidal antiestrogen drug, is used in the treatment of breast cancer. With its antiestrogen properties, it binds to estrogen receptors thus blocking estrogen dependent tumor growth. Estrogen, mainly the lack of, is instrumental in the cause of osteoporosis. At menopause, the lack of estrogen causes an increase in bone loss. Tamoxifen in a hypoestrogenic environment, post menopause, appears to have estrogen like effects and inhibits bone resorption. In vitro studies, however, demonstrate that Tamoxifen in the presence of estrogen actually inhibits the beneficial effects of estrogen on bone metabolism. This study will help to evaluate the beneficial effects of estrogen on bone metabolism. Monocytes will be isolated from whole blood and placed in culture. While in culture we will study the cytokines (substance released from inflammatory cells such as monocytes) which modulate bone resorption. These cytokines may be regulated by estrogen and/or Tamoxifen.